Articles you may be interested in X-ray excited luminescence of cuprous iodide single crystals: On the nature of red luminescence
The ionic conductivity of undoperl and doped BaFCl single crystals is measured. I n BaFCI, the measurements are performed parallel and perpendicular to the crystallographic c-axis. Incorporation of monovalent impurities (TI, Na) enhances the conductivity while it decreases by doping with trivalent impurities (Gd). The results indicate that BaFCl has anionic conduction via halide ion vacancies and that the thermally generated lattice defects are of Schottky type. The probable mechanism for the conduction process in these crystals is discussed on the basis of structural considerations of the unit cell.Die Ionenleitfahigkeit von undotierten und dotierten BaFCI-Einkristallen wird gemessen. I n BaFCl werden die Messungen parallel und senkrecht zur c-Achse durchgefuhrt. Der Einbau der monovalenten Storstellen (TI, Na) erhoht die Leitfahigkeit wiihrend sie durch Dotierung mit trivalenten Stijrstellen (Gd) verringert wird. Die Ergebnisse zeigen, daB in BaFCl anionische Leitfiihigkeit uber Halogenionenleerstellen erfolgt und die thermisch erzeugten Gitterdefekte vom Schottky-Typ sind. Der wahrscheinliche Mechanismus fur den LeitfahigkeitsprozeB in diesen Hristallen wird auf der Grundlage von Strukturbetrachtungen der Einheitszelle diskutiert.
We develop a higher-order perturbation theory for large-scale structure formation involving a free-streaming hot or warm dark matter species. We focus on the case of mixed cold dark matter and massive neutrinos, although our approach is applicable also to a single warm dark matter species. In order to capture the suppressed growth of neutrino density perturbations on small scales, we account for the full momentum dependence of the phase space distribution using the Vlasov equation, and derive from it a formal closed-form nonlinear equation for the neutrino density. Using a systematic perturbative expansion of this equation we compute high-order corrections to the neutrino density contrast without the explicit need to track the perturbed neutrino momentum distribution. We calculate the leading-order total matter bispectrum for several neutrino masses. Using our result as a benchmark, we test the accuracy of the fluid approximation and a linear approximation used in perturbative and N -body analyses, as well as a new hybrid approach that combines the exact linear evolution with the nonlinear structure of the fluid equations. Aiming at 1% accuracy, we find that the total matter bispectrum with a low neutrino mass m = 0.046 eV can be reproduced by all but the fluid approximation, while for larger neutrino masses m = 0.46 → 0.93 eV only the hybrid approach has the desired accuracy on a large range of scales. This result serves as a cautionary note that approximate nonlinear models of neutrino clustering that reproduce the gross features of some observables may not suffice for precision calculations, nor are they guaranteed to apply to other observables. All of the approximation schemes fail to reproduce the bispectrum of the neutrino density perturbations at better than 20% accuracy across all scales, indicating that an exact treatment of nonlinear neutrino perturbations is necessary.
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